1. Field of the Invention
The present invention pertains to flow control valves and more particularly to such valves which are suitable for controlling fluids at high pressures and flow rates.
2. Description of the Related Art
A typical prior art flow control valve includes a stem having a cone mounted on the lower end thereof which is movable toward and away from an orifice for regulating flow therethrough. The cone is received in a housing cavity which is in fluid communication with an inlet and an outlet. In operation, fluid enters the inlet and leaves the outlet at a reduced pressure and/or flow rate depending on the relative positions of the cone (which is set by turning the stem) and the orifice.
Such prior art valves suffer from several disadvantages. Under extremely high flows and pressures, large axial forces are exerted on the stem making the same very difficult, if not impossible, to adjust when fluid is flowing through the valve. Flow through such valves is typically turbulent rather than laminar thereby increasing wear on the valve.
Such prior art valves are also relatively imprecise in that the same orifice opening may not be obtained when the stem is rotated to different angular positions and thereafter returned to a previous angular position. In other words, a precise valve setting may not necessarily be repeatedly obtained. This is especially true when dealing with valves designed for high flow rates and pressures. Stem threads which will withstand such flows and pressures must be relatively deep and wide. Thus, the maximum number of threads per axial inch is limited. This limitation on the maximum number of threads per inch limits the precision with which the valve can be repeatedly reset to obtain a selected flow rate through the valve.